Laser welding plastic tubes

ABSTRACT

A method of welding a plastic end member to an unstepped, plastic tubular body which comprises positioning the end member within the body and then irradiating the area to be welded with a laser beam for a specified time sufficient to achieve the desired weld while simultaneously imparting relative rotational motion between the beam and the area to be welded.

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TAR 3 M 69 i 1. 17

United States Patent 1 Bowen et al.

LASER WELDING PLASTIC TUBES Inventors: William Edmund Bowen, Trenton;

Clifford Clayton Goehring, Princeton, both of NJ.

Assignee: American Can Company,

Greenwich, Conn.

Filed: Dec. 30, 1971 Appl. No.:-2l4,31l

US. Cl. 156/69, 156/272 Int. Cl. 1329c 27/00, 13290 19/02 Field oiSearch 156/272, 69

References Cited UNITED STATES PATENTS Hood et a1. 156/69 1 Oct. 30,1973 3,700,513 10/1972 Haberhauer et a1 156/272 3,560,291 2/1971 Fogliaet al. 156/272 OTHER PUBLICATIONS Modern Plastics; Vol. 46, No. 5, May1969 p. 71-74.

Primary Examiner-Douglas J. Drummond Atorney-Robert P. Auber et a1.

[57] ABSTRACT A method of welding a plastic end member to an unstepped,plastic tubular body which comprises positioning the end member withinthe body and then irradiating the area to be welded with a laser beamfor a specified time sufficient to achieve the desired weld whilesimultaneously imparting relative rotational motion between the beam andthe area to be welded.

8 Claims, 5 Drawing Figures INTENSITY PAIENIEBnmo ms F lG.l

- INTERFACE 0.50

DEPTH -(IN.)

FIG.3

FIG. 4 23 ISH/ FIG.2

BACKGROUND OF THE INVENTION The present invention relates to laserwelding plastic end members to unstepped, plastic, tubular bodies, andmore particularly to high speed welding of plastic squeeze tube heads toplastic bodies (sleeves).

Existing techniques for forming both rigid and flexible plasticcontainers include vacuum forming, injection molding and blow molding,among others. One present method for forming squeeze tubes comprisesinjection molding the head onto the tubular body (U.S. Pat. No.3,047,910). In another method a portion of the pre-formed head is heldin proximity to the body and molding apparatus is placed around both thehead and the body. Plastic injection molded into the area between thehead and body forms the remaining part of the head and joins thepre-formed head to the body (U.S. Pat. No. 3,356,263).

Still another method involves the assembling of a head and body,applying heat to the margins of the head and body where they are to bejoined to permit formation of beads, and then forming of the heatedmargins (beads) by sliding dies over the beads until the margins arecool enough to maintain the prescribed, unbeaded die shape (MakowskisU.S. Pat. No. 3,144,495).

In the above processes, there are presented several problems which areovercome by the present invention. In injection molding techniques, thespeed of production is reduced owing to the time required for injectionand cooling down of the plastic. Where dies or forming cavities must bebrought into alignment with mating parts, precision of the dies andparts and their motion becomes a critical factor. In the presentinvention, a minimum amount of material is heated to achieve weldingofthe end member and body, thereby allowing production rates to beincreased substantially. Little or no forming is required in the presentinvention owing to the precise nature of the welding process, addingfurthcr to the speed and efficiency of production. The instant inventionis a distinct improvement over the Makowski process, since it does notrequire any addi tional step to form a smooth, unbcaded container as nobeads are initially created.

SUMMARY OF THE INVENTION The present invention teaches a method of laserwelding a plastic end member to an unstepped, plastic tubular body, andcomprises the steps of positioning the end member within the body andthen irradiating the area to be welded with a laser beam for a specifiedtime sufficient to achieve the desired weld while simultaneouslyimparting relative rotational motion between the beam and the area to bewelded.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 4 is an enlarged, fragmentary,vertical, sectional view of the sleeve and squeeze tube head subsequentto the laser welding operation.

FIG. 5 is a partial enlargement of FIG. 4 showing the locking actionbetween the sleeve and squeeze tube head.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the preferred embodiment ofthe instant invention, the end member is a polyethylene squeeze tubehead 15 having a shoulder 14 and a skirt 13, while the tubular body is apolyethylene sleeve 17 (see FIG. 5). The source of energy forimplementing this invention is the laser, which is a form of lightamplifier that produces a highly collimated beam of intense radiation.The energy is essentially monochromatic, i.e., one wavclength. Thewavelength will depend upon the particular lasing medium utilized andcan range from the ultraviolet to the far infrared. Presently, the twomost valuable lasers for commercial applications requiring a continuoushigh power beam are the Carbon Dioxide (C0,) Gas Laser, wavelength 10.6microns, and the Neodymium-YAG Laser, wavelength 1.06 microns. CO, andNd-YAG lasers are available with output powers from a fraction of a wattto several hundred watts, and their beams can be focused to a fewthousandths of an inch or less. It has been found that powers in therange of to 200 watts are satisfactory for plastic welding with aC0,.laser.

Of primary importance in achieving a reliable weld having an appearanceeffecting high consumer acceptance is the control of the temperaturegradient in the members to be welded. The gradient will depend on theintensity and directivity of the radiant energy as well as on theabsorption and thermal characteristics of the material to be welded. Theabsorption of the beam by the plastic being irradiated will depend onthe absorption constant of the material at the wavelength of theirradiating beam. Since temperature is proportional to beam intensity,the temperature gradient of the irradiated material will followapproximately the exponential absorption law l=l,,e which gives the beaminten-.

sity (power per unit area) I at a distance d from a surface receivingincident beam intensity I for a material with an absorptioncoefficientia.

Applying the exponential absorption law, the plot in FIG. 1 shows theapproximate temperature profile in 0.030 inch thick polyethylene when itis irradiated with a 10.6 micron wavelength beam. The area closest tothe incident surface receives the greatest energy since the beam has notbeen attenuated by increments of thickness. The beam penetration (andthus the steepness of the temperature gradient) is a function of theabsorption constant a. The temperature at and near the incident surfaceis therefore higher than at the interface of the two 0.015 inch layersindicated by the dotted line in FIG. 1.

Since plastics are generally poor thermal conductors, the heating isvery localized. It is essential that temperature rise in the plastic andparticularly at its surface does not reach a value that will causedegradation or excessive flow of material. On the other hand, if a weldor fusion of materials is to be accomplished at an interface, such as ata 0.0l5 inch depth as in FIG. I, the temperature in that area must riseto the melting point of the material.

Experiments with low density polyethylene tubular bodies 0.014 inchthick, and polyethylene heads inserted into the bodies have shown thatdeformation can occur at the outer surface of the body when sufficientenergy is supplied to fuse the body and head during one revolution ofthe work piece. The radiation was from a C0, laser focused to a 0.030inch spot diameter and having an intensity of 0.17 megawatts per squareinch. Difficulty was also encountered in timing precisely the exposurenecessary to complete exactly one revolution so that no overlap of theweld would occur which would further deform the surface. Consequently,the laser apparatus was adjusted to rotate the workpiece at severaltimes the initial speed, while the exposure time was held constant, sothat the weld area passed under the beam several times at aproportionally higher speed. In affect, less energy per increment oftime was delivered to a given spot, but the same energy was delivered inthe total exposure interval. A good weld was produced with significantlyless deformation of the outer surface and a less clearly defined overlaparea.

It was found that placement of idler rollers against the weld area wasadvantageous in some cases. It is obvious that these would have asmoothing effect on the weld, but, more important was their action incooling the outer surface of the body. Conductive rollers such asaluminum aided in cooling the surface on each rotation after beamirradiation.

The above improvements in appearance can be explained by referring tothe earlier discussion and the graph of FIG. 1. By supplying energy tothe weld area at a rate and duration that will not cause degradation andby allowing surface cooling between periods of irradiation, the innerlayer of several layers of plastic can be heated to their fusiontemperature with minimal surface deformation. The technique of multipleexposure and roller cooling tends to flatten the temperature gradientpeak at the near surface without significantly affecting the interiortemperature.

In thermal bonding, pressure is usually an important parameter, and inmany plastic heat sealing methods it is necessary, beacause heat forsealing is supplied to the plastic from a hot roller or platen from ahot roller or platen contacting the workpiece. The pressure aids heattransfer by conduction and aids fusion by forcing together the membersto be welded. The laser beam can generate heat within the members to bewelded without contact, which is ideal for high speed fabrication.However, it is necessary that the interface of the members to be weldedbe in as intimate contact as possible to reduce the amount of meltingrequired to fuse the members. To fulfill this requirement, aninterference fit between the members to be welded is recommended. Such afit would result where the outer diameter of the skirt 13 is greaterthan the inner diameter of the sleeve 17. This type of fit producesrelative pressure between the members without contact of an externalelement. A variation of the interference fit is shown in FIG. 2, whereina raised ridge 11 is formed in the skirt 13 of the head 15, so that thelarger diameter of the raised. ridge 1] creats pressure against thesleeve 17. The ridge 11 serves several functions. First, it producespressure contact between the head 15 and the sleeve 17. Second, itprovides additional material in the weld area to compensate forreduction in the thickness of the sleeve 17 that may result fromshrinkage due to heating. Third, the projection of the raised ridge llinto the sleeve 17 yields a locking type action when the material of thebody 17 flows around the ridge 1 1. (See FIG. 5).

FIG. 3 shows representative apparatus for implementing the method ofthis invention. The sleeve 17 and the head 15 are assembled on arotating mandrel l6 and positioned so that the area to be welded is nearthe focus of a lens 19 that intercepts a laser beam 21. A pressureroller 23 is employed to remove heat and smooth the surface of the weld,but is not essential, es-

pecially with high density polyethylene.

In order to weld the sleeve 17 and the head 15 in the manner of thisinvention, it is preferred that the radiant energy pass through the mostproximate layer of material, being the sleeve 17 in this case, andpenetrate to the juncture of the sleeve 17 and head 15. This techniquewas utilized together with apparatus similar to that shown in FIG. 3 toweld a 0.875 inch diameter sleeve havinga wall thickness of 0.014 inchesto the skirt of a head (see FIG. 4). Sleeves and heads of both low andhigh density polyethylene, both clear and pigmerited, were used. Laserpower was watts focused to a 0.030 inch diameter spot at the weld area.The sleeves (and heads in turn) were rotated by a mandrel at 1,500revolutions per minute and the laser beam was turned on for 0.28seconds, the equivalence of seven revolutions of sleeve and head. Thefinished squeeze tubes held 40 p.s.i. of air pressure without leaking.

It should be noted that when materials are semitransparent to theirradiation wavelength being used, some amount of energy, depending onthe total thickness of the material, will travel through and exit at therear surface. A reflective backing at the rear surface can re-direct theexiting energy back through the material to gain greater utilization ofthe irradiating beam, and thereby further flatten the energydistribution curve. For the present invention, the underlying surface isusually a workpiece holder or mandrel. The surface of this fixture belowthe weld area should be polished to produce maximum reflection.

Another means has been confirmed to improve weld penetration in plasticsheet while producing less surface deformation. In this method, thecircular beam spot pattern is shaped by special focusing so that itsdimensions along the weld path is increased while the width remainsconstant; The energy density of the focused beam is thus reduced sincethe same power is spread over a larger area, but the work per unitlength does not change because the weld width has not been increased.Such beam elongation can be accomplished by employement of cylindricalor other special lenses, mirrors, or by utilization of off-axisastigmatism.

It should be noted that it is not necessary that the laser beam passthrough the most proximate layer of material. It is possible that thebeam could pass through an interior layer of material (i.e., from theinside to the outside) by means of special apparatus and manipulation ofthe workpiece. Such a technique would be useful where metal laminatesare being welded.

Although the invention has been described in reference to cylindricaltubes, it is also quite applicable to oval shaped tubes.

It is thought that the invention and many of its attendant advantageswill be under stood from the foreqoing description and it will beapparent that various changes may be made in the form, construction andarrangement of the parts of the article and that changes may be made inthe Steps of the method described andtheir order of accomplishmentwithout departing from the spirit and scope of the invention orsacrificing all of its material advantages. the form hereinbeforedescribed being merely a preferred embodiment thereof.

What is claimed is: l. A method of welding a plastic end member to anunstepped. plastic tubular body, comprising:

positioning the end member within the body in substantially the samerelative position desired in the finished article;

I irradiating the area to be welded with laser beam for a fraction of asecond sufficient to achieve the desired weld while a mandrelsimultaneously imparts relative rotational motion of at least'360between the beam and the area to be welded.

2. The method of claim 1 wherein said end member is a squeeze tube headand said body is a sleeve.

3. The method of claim 2 wherein the outer diameter of the skirt of saidhead is greater than the inner diameter of the sleeve, thereby producingan interference fit between the head and sleeve.

4. The method of claim 3 wherein the laser beam has a wavelength of 10.6microns.

5. The method of claim 4 wherein the laser beam is elongated in thedirection of the weld path.

6. The method of claim 5 wherein the head sleeve are both polyethylene.

7. The method of claim I wherein the fraction is about one-fourth.

8. The method of claim 7 wherein the rotational motion consists of aboutseven revolutions of the end member and body relative to the beam.

' i it t I and

1. A method of welding a plastic end member to an unstepped, plastictubular body, comprising: positioning the end member within the body insubstantially the same relative position desired in the finishedarticle; irradiating the area to be welded with laser beam for afraction of a second sufficient to achieve the desired weld while amandrel simultaneously imparts relative rotational motion of at least360* between the beam and the area to be welded.
 2. The method of claim1 wherein said end member is a squeeze tube head and said body is asleeve.
 3. The method of claim 2 wherein the outer diameter of the skirtof said head is greater than the inner diameter of the sleeve, therebyproducing an interference fit between the head and sleeve.
 4. The methodof claim 3 wherein the laser beam has a wavelength of 10.6 microns. 5.The method of claim 4 wherein the laser beam is elongated in thedirection of the weld path.
 6. The method of claim 5 wherein the headand sleeve are both polyetHylene.
 7. The method of claim 1 wherein thefraction is about one-fourth.
 8. The method of claim 7 wherein therotational motion consists of about seven revolutions of the end memberand body relative to the beam.